1. Field Of The Invention
This invention relates to a motor driving device used for driving a motor in the forward and reverse rotational direction.
2. Description Of The Prior Art
Heretofore, there have been various types of motor driving devices which use different circuit formation. One known formation uses the circuit formation shown in FIG. 2 for example.
A motor driving device 101 shown in FIG. 2 has circuit formation comprising a switching part Q1 which is a p-type field effect transistor (hereinafter referred to as "FET") for supplying a current in the forward rotational direction to a motor 102 rotatable in the forward and reverse direction, a switching part Q2 which is a p-type FET for supplying a current in the reverse rotational direction to the motor 102, a switching part Q3 which is a n-type FET for grounding the current in the forward rotational direction through the motor 102, a switching part Q4 which is a n-type FET for grounding the current in the reverse rotational direction through the motor 102, a control means housed in a microcomputer 103 for rotating the motor 102 in the forward and reverse direction by controlling the respective switching parts Q1 to Q4 into an ON-state or OFF-state, a npn-type transistor Tr1 for generating a negative voltage at the gate of switching part Q1, and a npn-type transistor Tr2 for generating a negative voltage at the gate of switching part Q2. Switching parts Q1 to Q4 are connected with both terminals of said motor 102 in H-bridge connection, wherein the switching parts Q1 and Q4 are connected in series between a power source and ground. Switching points Q1 and Q4 are similarly connected in series between power and ground.
The motor driving device 101 is so designed as to drive the motor 102 in the forward or reverse rotation by turning on or off the respective switching parts Q1 to Q4 according to instructions from the control means housed in the microcomputer 103.
However, in the above mentioned motor driving device 101, there is the possibility of some failure in the microcomputer 103 by, for example, overvoltage. If the switching parts Q1 and Q4 or the switching parts Q2 and Q3 are turned into the ON-state at the same time, an excess current flows directly between the power source and the ground through the switching parts Q1 and Q4 or the switching parts Q2 and Q3. Accordingly, there is a problem since the switching parts Q1 to Q4 are in danger of breaking down.